In the prior art, following various techniques are developed.
According to patent document 1, in an ozone generator system, a raw material gas is supplied from a first raw material supply system for supplying a specified flow rate from an oxygen cylinder with a purity of 99.995% or higher, and from a second raw material supply system for supplying a specified flow rate of second raw material gas (nitrogen, helium, argon, or carbon dioxide) with a purity of 99.99% or higher, a high AC voltage is applied between electrodes, silent discharge (dielectric barrier discharge) is caused between the electrodes through a dielectric, and the raw material gas is transformed into an ozone gas. It is disclosed that although the cause of a time-varying reduction phenomenon of ozone concentration is not clear, the time-varying reduction phenomenon exists in the ozone gas once generated by the generator under high purity oxygen, and as means for suppressing the time-varying reduction, it is effective to add a nitrogen gas or the like to the high purity oxygen.
Patent document 2 discloses that a mixture ratio of an oxygen gas as a raw material gas of an ozone apparatus to a nitrogen gas is set in a range of from 1:0.0002 (200 ppm) to 0.0033 (3300 ppm). FIG. 2 of the patent document 2 shows a characteristic of the amount of addition of nitrogen gas and the concentration of ozone obtained by the ozone generator system, and as the amount of addition of nitrogen at which sufficient ozone concentration (about 100 g/m3 or more) is obtained, the mixture ratio is set to 1:0.0002. In order to suppress the amount of generation of nitrogen oxide as a reaction poisonous substance from the generator to be small, the mixture ratio is set to 1:0.0033 or less. It is disclosed that when the oxygen raw material gas in which the amount of addition of nitrogen is 100 ppm or less is used, the ozone concentration of 20 g/m3 (9333 ppm) is merely obtained, and the ozone concentration which is ⅙ or less of the ozone concentration of 120 g/m3 (56000 ppm) at the time of a nitrogen additive rate of 3300 ppm is merely obtained. Besides, in the specification, it is disclosed that although an argon gas, instead of the nitrogen gas, is added to the high purity oxygen, the ozone concentration of about 20 g/m3 (9333 ppm) is merely obtained independently of an argon mixture ratio, and the argon gas does not have an effect to raise the ozone concentration.
Besides, according to patent document 3, in an ozone generator system, a TiO2 film is formed on a discharge surface of a dielectric. Instead of the addition of high purity nitrogen gas, titanium oxide having a metal element ratio of 10 wt % is coated on the discharge surface of the dielectric in the generator.
Besides, in patent document 4, it is proposed that in an ozone apparatus which can obtain a maximum ozone concentration of 180 g/m3, the amount of addition of nitrogen is made 0.01% to 0.5% in order to suppress the time-varying reduction of ozone concentration.
In the prior art, with respect to the mechanism of generating the ozone gas by silent discharge, it is said that the generation is carried out by following reaction equations.e+O22O+e (dissociation of oxygen)  R1;O+O2+MO3+M  R2;
(ozone generation based on triple collision by oxygen atom and oxygen molecule)e+O3O+O2+e (electron collision decomposition)  R3;O3+heat TO+O2 (heat decomposition)  R4;O3+NO2+N1(decomposition of ozone by impurity)  R5;
Incidentally, N1 denotes what is different from N.
The generation of the ozone gas is such that the oxygen molecule is dissociated into the oxygen atoms in R1, and the ozone is generated based on the triple collision by the oxygen atom and the oxygen molecule in R2.
As the decomposition of the generated ozone, the electron collision decomposition of R3, the heat decomposition of R4, the decomposition of ozone by the impurity of R5, or the like is conceivable.
As the ozone gas which can be extracted from the generator, the ozone gas is obtained according to the balance state of the reaction equations of R1 to R5. That is, the ozone gas can be extracted by a following equation.extracted ozone=(R1*R2)−(R3+R4+R5+ . . . )
Besides, in the prior art, it is stated that in the case of the high purity oxygen, with respect to the ozone generated by the ozone generation mechanism, since the ozone concentration is reduced with the passage of time during the operation, the nitrogen gas is added to the raw material gas, or TiO2 as the photocatalyst is applied to the discharge electrode surface, so that a following reaction occurs, and the time-varying reduction of the ozone concentration is prevented.O3*+N2O3O3*+TiO2O3
Patent document 1, patent document 2 and patent document 3 are for stably obtaining the ozone concentration at a relatively low ozone concentration of about 120 g/m3.
Incidentally, in the respective conventional techniques, different phenomena as set forth below are described. Although patent document 1 discloses that a gas of helium, argon, or carbon dioxide is also effective as a gas other than the nitrogen gas addition, patent document 2 discloses that in the case of the high purity oxygen, the argon gas is not effective.
Although patent document 1 discloses that the amount of addition of the second raw material gas is made 10000 ppm to 100000 ppm, patent document 2 discloses 200 ppm to 2300 ppm which is different.
Patent document 1 discloses that in the high purity oxygen, the concentration is reduced by the operation for about one hour, while patent document 3 discloses the concentration reduction after the operation for about 7 hours, which is different.
Besides, patent document 1 discloses at column 6, line 49 to column 7, line 2 that as an ozone concentration immediately after the start of the operation, data is shown in FIG. 6 in which an ozone concentration of only 75 g/m3 is obtained at a time of a percentage content of 0 vol %, while FIG. 5 shows that an ozone concentration immediately after the start of the operation in high purity oxygen is a maximum concentration of 143.5 g/m3 (see Table 3). The two experimental data indicate quite different values and phenomena, and exhibit very unclear facts.
As stated above, in the conventional technique in which with respect to the ozone generated in the apparatus, the nitrogen gas or the like is added to the oxygen gas in order to suppress the time-varying reduction of the ozone concentration, the results and effects vary according to the conditions, and although an experimental verification was made for patent document 1, patent document 2, and patent document 3, patent document 1 and patent document 3 could not be substantiated, and it turned out that the addition of a single noble gas (helium, neon, argon, xenon, etc.) other than nitrogen was ineffective.
Both patent document 1 and patent document 4 disclose that the reduction of the ozone concentration is the time-varying reduction, however, it is disclosed that when it is once reduced, it does not return to the original ozone concentration. From the recitation that the concentration does not return to the original ozone concentration, it can not be judged to be the time-varying reduction, and the role of the addition of nitrogen is not clear.
Further, when the nitrogen is added at an additive rate of approximately 0.15% (1500 ppm) or more, in addition to the ozone gas, a large amount of NOX by-product gas such as N2O5 or N2O is generated by the silent discharge.N2O5+H2O2HNO3OH+NO2+MHNO3+M
Besides, when a large amount of NOX by-product is produced, a nitric acid (HNO3) cluster (vapor) is generated by the reaction of the NOX gas component and moisture contained in the raw material gas, and the ozonized gas is extracted in such a state that a trace amount of NOX gas and nitric acid cluster, together with oxygen and ozone gas, are mixed. When the amount of the trace amount of nitric acid cluster contained is several hundred ppm or more, there are problems that rust of chromium oxide or the like is deposited by nitric acid on the inner surface of a stainless pipe as an ozone gas outlet pipe, a metal impurity is mixed into a clean ozone gas, the metal impurity in a reaction gas for a semiconductor manufacturing apparatus has a bad influence on the manufacture of a semiconductor, and the trace amount of the generated nitric acid cluster has a bad influence as a reaction poisonous substance on “an etching process of a silicon oxide film by ozone” or “ozone water washing of a wafer or the like” of the semiconductor manufacturing apparatus.
In the ozone apparatus of the conventional technique, the concentration of the extracted ozone is low, and in order to extract ozone with a high concentration of 200 g/m3 or more, there is only a method of increasing the nitrogen additive rate or a method of decreasing the gas flow rate. In the method of increasing the nitrogen additive rate, as described above, there is a problem that the by-product gas of NOX is increased.
Besides, when the gas flow rate is decreased, there are problems that the amount of ozone generation is extremely lowered, and production efficiency on the side of using the ozone becomes worse.
Further, in the newest “etching apparatus of an oxide film by ozone” or “ozone water washing of a wafer or the like”, a high ozone concentration of 200 g/m3 or more is needed, and with respect to the amount of ozone generation, there is a request for an ozone apparatus having an ozone capacity of several tens g/h or more on an economically viable basis in production on the user side. Further, in a semiconductor manufacturing apparatus, an apparatus which produces less reaction poisonous material, such as nitric acid, has been needed.
Besides, although a trace amount, about 1%, of N2 gas is added in order to increase the generation efficiency of an ozone gas, the N2 gas is transformed into NOX or nitric acid cluster (vapor) by discharge in the generator.
Thus, in the discharge space (discharge region), as the gas flow velocity becomes low, or the injected discharge power becomes high, the amount of generation of NOX as the nitrogen oxide is increased, and therefore, there are problems that the ozone generation efficiency is lowered, and the concentration of the extracted ozone is reduced.
Next, as specific main production apparatuses using high concentration ozone gas and products obtained by the production apparatuses, the following are enumerated.
TABLE 1Main production apparatus using ozone gas and productsfield of productionapparatusobtained productfunctionchemical vaporsemiconductorconductive thin filmdeposition apparatus,insulating thin filmALD thin film depositiondielectric thin filmapparatussemiconductor thin filmcapacitorhigh dielectric constantthin filmflat panelconductive tin filminsulating thin filmdielectric thin filmsemiconductor thin filmsolar cellconductive thin filminsulating thin filmdielectric thin filmsemiconductor thin filmmagnetic tapehigh magnetic thin filmsuperconductingsuperconducting thin filmthin filmozone condensingultra highozone condensationapparatusconcentration ozonegaspulp bleaching apparatuspaperozone bleaching
FIG. 24 shows an example of a conventional chemical vapor deposition apparatus (that is, CVD apparatus: Chemical Vapor Deposition) for forming a thin film by using a high concentration ozone gas or an ALD thin film deposition apparatus (Atomic Layer Deposition).
In FIG. 24, reference numeral 600 denotes a CVD apparatus or an ALD deposition apparatus apparatus to obtain a metal vapor by laser ablation; 601, a laser apparatus; 602, a laser beam diaphragm lens; 603, a chamber; 604, a beam inlet port; 607, a beam inlet window; 605a, an ozone gas inlet port; 605b, a noble gas inlet port; 606, a gas exhaust port; 608, a table for a processed material; 610, a processed material (semiconductor wafer, etc.); 612, a stand; 611, a metal target material for a thin film of noble metal such as platinum, ruthenium or palladium; A3000, an ozone gas supply system; and 618, a vacuum apparatus. Incidentally, 10A denotes a noble gas cylinder; 617, a vacuum valve; and 619, exhaust.
In the conventional CVD apparatus or the ALD thin film deposition apparatus, a gas of mixture of an oxygen gas from an oxygen gas cylinder 10 and a nitrogen gas from a nitrogen cylinder 10B in a range of about 0.01 to 1% with respect to the oxygen gas is supplied to an ozone generator system A300, a high concentration ozone gas is generated in the ozone generator system, the high concentration ozone gas is inputted to the CVD apparatus or the ALD thin film deposition apparatus, and an oxidation reaction process of ozone is performed. The operation of the apparatus is such that the processed material 610 is mounted on the processed material table 608, vacuum drawing is performed by the vacuum apparatus 618, and moisture or the like adhered to the surface of the processed material 610 is removed. Subsequently, an ozone gas of about 100 g/m3 is introduced into the chamber 603 in a negative pressure state, the temperature is raised up to several hundred degrees by a heater in the processed material table 608 and a temperature adjustment part 609, a carbon compound, moisture, hydrogen compound and the like adsorbed on the surface of the processed material 610 are subjected to a thermal reaction process by the ozone gas, and a cleaning process of the surface of the processed material 610 is performed (0. cleaning step).
At a next step, in the evacuated chamber 603, a pulse laser beam 613 having intense energy is focused on and is made to impinge on the thin film target material 611 as the thin film material in the chamber from the laser apparatus 601 mounted outside, so that a metal vapor 615 is released by local heating from the thin film target material 611 into the chamber, the low pressure metal vapor is made to fill it, and metal particles of the order of from submicron to several microns are deposited onto a surface at an atomic layer level by the temperature control of the processed material mounted on the processed material table 608 (1. deposit step). With respect to the metal deposited onto the surface of the processed material at the atomic layer level, a high concentration ozone gas of about 300 g/m3 in a negative pressure state is introduced into the chamber, the temperature is raised up to several hundred decrees by the heater in the processed material table 608 and the temperature adjustment part 609, and the deposited metal is transformed into metal oxide (2. ozone oxidation reaction step).
At a final step, in a state where the inside of the chamber is made to be filled with a noble gas as an inert gas, or the like, a heat treatment at a specified temperature is performed by the heater in the processed material table 608 and the temperature adjustment part 60, and the metal oxide is made an effective metal oxide crystal (3. annealing step). The above steps of 1. deposit step→2. ozone oxidation reaction step→3. annealing step are repeated until the deposited thin film comes to have a desired thickness, and the thin film effective in function is formed. Although the process of forming a thin film such as a semiconductor includes, in addition to the above steps, various complicated steps such as a doping step, an etching step, and a resist peeling step, they are omitted here.
As products using thin films, there are a capacitor mounted on a board of an electronic apparatus, a semiconductor element, a flat panel as a display part of a television, a solar battery cell used for a solar battery, a superconducting thin film element, and a magnetic storage tape.
In the thin films used for these products, reduction in film thickness is required for purposes as follows:
i) improvement in integration
ii) reduction in cost of element
iii) improvement in function
iv) reduction in electric power.
In order to realize products having achieved the objects as stated above, with respect to requested performance of a thin film itself, one having following functions is required.
(1) semiconductor thin film
(2) insulating thin film
(3) oxide metal thin film
(4) ferroelectric thin film for a capacitor or a semiconductor,
(5) ferromagnetic thin film for magnetic recording
(6) thin film as an optical material for a photoelectric device
(7) superconducting thin film
As the semiconductor thin film of (1), there is a silicon oxide thin film. As the insulating thin film of (2), attention is given to a thin film of ZrO2, HfO2, or Ln2O3 excellent in insulation. As the oxide metal thin film of (3), there is RuO2 or SrRuO3 instead of platinum and copper. As the ferroelectric thin film of (4), there is Pb(ZrxTi1-x)O3 or (BaxSr1-x)TiO3 for a nonvolatile memory. As the ferromagnetic thin film of (5), there is Y3Fe5O12. As the thin film as the optical material of (6), attention is given to a high speed optical switching function of LiNbO3 or the like, and attention is given also to a thin film as a waveguide. As the superconducting thin film of (7), there is a metal oxide such as YBa2CuO7.
Any of these thin films are obtained by crystal growth of metal oxide of noble metal as transition metal of Group IV, or GroupIII-V under a specific environment. In order to obtain these metal oxides, there is required a thin film realized by only high thermodynamic oxidation capacity (oxidation comparable to high pressure oxygen corresponding to a pressure of 1018 atmospheres in an equivalent oxygen partial pressure) of the ozone gas, and it can be hardly realized unless the ozone gas is used.
A conventional CVD apparatus and an ALD thin film deposition apparatus to obtain a metal oxide thin film having the high function as stated above have problems as set forth below.
i) Performance quality of the thin film is poor.
ii) Performance of the thin film is uneven.
iii) Deposition speed of the thin film is low.
As the cause of i) and ii), a metal impurity, a carbon impurity, a nitrogen impurity, hydrogen, or moisture is mixed at respective steps in the apparatus, and there are problems of the insulation of the thin film element, the increase of leak current, the fluctuation of performance, the deterioration of mechanical adhesion of the thin film itself, and the like.
In a conventional ozone gas condensing apparatus using a high concentration ozone gas, a high concentration ozone gas obtained from an ozone generator system is made to pass through a tank filled with silica gel cooled to about −60° C. to −100° C. to form liquefied ozone, and it is made to be adsorbed (adsorption step) by the filling silica gel, and then, the adsorbed liquefied ozone is heated up to approximately a room temperature, a carrier gas such as oxygen is made to flow through the tank filled with the silica gel or the like, the liquefied ozone is evaporated (desorption step), and the super-high concentration ozone gas higher than the high concentration ozone gas obtained from the ozone generator system is obtained. In this ozone condensing apparatus, when an impurity such as nitrogen or nitrogen oxide (NOX) is contained in the ozone gas, not only the ozone gas, but also NOX contained in the gas is liquefied, and the adsorbed NOX is not desorbed in the desorption step but is accumulated on the silica gel, and there is a problem that the condensing ability of the condensing apparatus is lowered.
In conventional bleaching of pulp, chlorine bleaching has been the mainstream. However, at the time of pulp bleaching, since an organochlorine compound such as harmful dioxin is discharged, there occurs a problem from the viewpoint of environment, and attention is given to an ozone bleaching apparatus which has bleaching ability and does not discharge a harmful material. However, a large ozone apparatus is hard to realize, and there has been a fear that since nitrogen oxide is contained in the ozone gas, a pipe is broken due to corrosion of the pulp bleaching apparatus, and pulp fibers are damaged. Besides, in the case where nitrogen gas is not added to the ozone generator system, a sufficient amount of ozone generation is not obtained, and there have been problems that the ozone generator system becomes large, electric power consumption becomes large, and an economical merit of the ozone bleaching apparatus is lost.
Patent document 1: JP-B-6-21010 (pages 1 to 4, FIG. 1)
Patent document 2: Japanese Patent No. 2641956 (pages 1 to 4, FIGS. 2 to 3)
Patent document 3: JP-A-11-21110
Patent document 4: Japanese Patent No. 2587860